The present invention pertains to acetabular reamers and more particularly pertains to an acetabular reamer cup.
Acetabular reamers are used by surgeons to prepare pelvis bones for insertion of artificial hip joints. An acetabular reamer is rotated to cut a cavity into the bone into which the socket portion of the artificial hip joint can be inserted. Dimensions and shape of the cavity cut are critical as the tolerances between the cavity and the socket portion of an artificial hip joint must be small to ensure proper function. This is especially true with the newly available "cementless" hip joints. Before "cementless" hip joints, the socket portion of the joint was cemented into the cavity in the pelvis bone. In the "cementless" joint, the socket portion is frictionally fit into the cavity, placing new importance upon accurate cavity dimensions and tolerances.
An acetabular reamer is composed of an acetabular reamer cup mounted on a tool driver, which in turn is mounted in the chuck or collet of a portable drill or flexible powered shaft. Acetabular reamer cups have a complex arrangement of precisely shaped cutting surfaces extending outward from an essentially hemispherical shell. Acetabular reamer cups are separable from their tool drivers for changing cup size prior to or during surgery, cleaning, and sharpening.
Acetabular reamers must be capable of producing cavities with very close tolerances and must also minimize any risk of causing contamination. Acetabular reamer cups have precise dimensions and are light in weight and must fit on an appropriate tool driver with a minimum of free play and must be quick and easy to install and remove without tools.
In the past, acetabular reamer cups have failed to provide a microscopically smooth surface with ideal tolerances for the implant. Acetabular reamer cups currently in use are characterized by generally rough, convex surfaces possessing a multitude of cutting edges. Unlike the present invention, the cutting edges are curved tangentially and result in an overall knobby surface. Thus, microscopically, upon rotation of the reamer cup, the knobby surface tends to grab and jump and chip resulting in a gouged and rough and uneven surface cavity whereby the accuracy of tolerances between the cavity and the implant ball that is gained by the precision in manufacture is thereby lost due to the undesirable cutting action and, in a large degree, the difficulty in operating and controlling precise cutting action of the knobby cup.
Some previous acetabular reamers have used an openbottom acetabular reamer cup gripped on the tool driver by means of a flange and slot and an opposed springloaded ball catch, like that on a socket wrench or socket driver. This presents a problem in that the catch tends to trap dried blood, which is very difficult to remove during cleaning. An additional problem is that unless tolerances of cups and tool drivers are made very close, at great cost, there is considerable free play between a cup and its tool driver. This increases wear and decreases the precision of the tool.
An alternative acetabular reamer, described in U.S. Pat. No. 4,811,632, utilizes a convex-bottomed acetabular reamer cup having a large central opening complementary in shape to a flange on the tool driver. Since the tool driver also grips the cup with a clamping action, extremely close tolerances are not required to prevent free play between the cup and driver. The convex bottom of the cup eliminates internal ninety degree angles, which could catch contaminants and the large central opening permits easy cleaning. The acetabular reamer cup is, however, complex in shape and expensive and, like all acetabular reamer cups, difficult to resharpen.
It is therefore highly desirable to provide an improved acetabular reamer cup.
It is also highly desirable to provide an improved acetabular reamer cup which fits on a tool driver with a minimum of free play.
It is also highly desirable to produce an acetabular reamer cup having a smooth cutting action.
It is also highly desirable to provide an improved acetabular reamer cup that has a controlled cutting action that will yield a surface cavity of more precise dimensions.
It is also highly desirable to provide an improved acetabular reamer cup that will produce a smooth surface with precise dimensions with less reliance on the operator's skill and ability to control the tool.
It is also highly desirable to provide an improved acetabular reamer cup which is precise in size, light in weight and inexpensive.
It is also highly desirable to provide an improved acetabular reamer cup which is quick and easy to install and remove from a tool driver without tools.
It is finally highly desirable to provide an improved acetabular reamer cup which meets all of the above desired features.